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how to detect the value angle of rotation object ?

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i have a image with 4 object, i want to know how much the angel of rotation object. please help, thanks


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Accepted Answer

Image Analyst
Image Analyst on 18 Apr 2016
Try this:
clc; % Clear the command window.
close all; % Close all figures (except those of imtool.)
clear; % Erase all existing variables. Or clearvars if you want.
workspace; % Make sure the workspace panel is showing.
format long g;
format compact;
fontSize = 20;
% Check that user has the Image Processing Toolbox installed.
hasIPT = license('test', 'image_toolbox'); % license('test','Statistics_toolbox'), license('test','Signal_toolbox')
if ~hasIPT
% User does not have the toolbox installed.
message = sprintf('Sorry, but you do not seem to have the Image Processing Toolbox.\nDo you want to try to continue anyway?');
reply = questdlg(message, 'Toolbox missing', 'Yes', 'No', 'Yes');
if strcmpi(reply, 'No')
% User said No, so exit.
% Read in gray scale demo image.
folder = pwd
baseFileName = '1.jpg';
% Get the full filename, with path prepended.
fullFileName = fullfile(folder, baseFileName);
% Check if file exists.
if ~exist(fullFileName, 'file')
% File doesn't exist -- didn't find it there. Check the search path for it.
fullFileNameOnSearchPath = baseFileName; % No path this time.
if ~exist(fullFileNameOnSearchPath, 'file')
% Still didn't find it. Alert user.
errorMessage = sprintf('Error: %s does not exist in the search path folders.', fullFileName);
grayImage = imread(fullFileName);
% Get the dimensions of the image.
% numberOfColorBands should be = 1.
[rows, columns, numberOfColorChannels] = size(grayImage);
if numberOfColorChannels > 1
% It's not really gray scale like we expected - it's color.
% Convert it to gray scale by taking only the green channel.
grayImage = grayImage(:, :, 2); % Take green channel.
% Display the image.
subplot(2, 2, 1);
imshow(grayImage, []);
title('Original Grayscale Image', 'FontSize', fontSize, 'Interpreter', 'None');
% Set up figure properties:
% Enlarge figure to full screen.
set(gcf, 'Units', 'Normalized', 'OuterPosition', [0 0 1 1]);
% Get rid of tool bar and pulldown menus that are along top of figure.
set(gcf, 'Toolbar', 'none', 'Menu', 'none');
% Give a name to the title bar.
set(gcf, 'Name', 'Demo by ImageAnalyst', 'NumberTitle', 'Off')
% Let's compute and display the histogram.
subplot(2, 2, 2);
histogram(grayImage, 0:256);
grid on;
title('Histogram of original image', 'FontSize', fontSize, 'Interpreter', 'None');
xlabel('Gray Level', 'FontSize', fontSize);
ylabel('Pixel Count', 'FontSize', fontSize);
xlim([0 255]); % Scale x axis manually.
% Threshold and binarize the image
binaryImage = grayImage > 128;
% Display the image.
subplot(2, 2, 3);
imshow(binaryImage, []);
axis on;
title('Binary Image', 'FontSize', fontSize, 'Interpreter', 'None');
% Label the image
labeledImage = bwlabel(binaryImage);
% Get the orientation
measurements = regionprops(labeledImage, 'Orientation', 'MajorAxisLength', 'Centroid');
allAngles = -[measurements.Orientation]
hold on;
for k = 1 : length(measurements)
fprintf('For blob #%d, the angle = %.4f\n', k, allAngles(k));
xCenter = measurements(k).Centroid(1);
yCenter = measurements(k).Centroid(2);
% Plot centroids.
plot(xCenter, yCenter, 'r*', 'MarkerSize', 15, 'LineWidth', 2);
% Determine endpoints
axisRadius = measurements(k).MajorAxisLength / 2;
x1 = xCenter + axisRadius * cosd(allAngles(k));
x2 = xCenter - axisRadius * cosd(allAngles(k));
y1 = yCenter + axisRadius * sind(allAngles(k));
y2 = yCenter - axisRadius * sind(allAngles(k));
fprintf('x1 = %.2f, y1 = %.2f, x2 = %.2f, y2 = %.2f\n\n', x1, y1, x2, y2);
plot([x1, x2], [y1, y2], 'r-', 'LineWidth', 2);


Image Analyst
Image Analyst on 24 Apr 2016
One way is to call impixelinfo() after you display the image. Then you can mouse around over the image and see what the label numbers are. Another way is to simply give the (row, column) coordinate/index to the labeled matrix. Or you could use ginput().
ElizabethR on 24 Apr 2016
thaks for answare. but i mean is like this code
[sortedAreas, sortIndexes] = sort(allAreas, 'descend');
how to get the value of sortIndexes ??
Image Analyst
Image Analyst on 24 Apr 2016
The function sort() returns it as one of the output arguments, so you already have it.

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More Answers (1)

Meghana Dinesh
Meghana Dinesh on 15 Apr 2016
You can find the major axes of all the four objects. The direction of each of their major axis gives the angle of rotation.


ElizabethR on 15 Apr 2016
thanks Meghana for answare my question.. but, how to find the major axes of all the four object ?

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